Electro-confinement nano-membrane desalination

J. Ma, W. Wei, G. Qin
Beihang University,

Keywords: nano-membrane, confinement effect, electric field, desalination


Electro-confinement nano-membrane desalination (ECMD), combining electric field effects and confinement effects in nanochannel, was reported for Na2SO4 removal. This reactor applied nano-porous carbon membranes as electrode and the asymmetric carbon membrane with average pore size of 8.3 nm was prepared by organic sol-gel method. The thickness of the top layer supported by macroporous support is 35 μm. When the carbon membrane was set as cathode, the rejection of SO42- was 94.89% while the removal of Na+ was less than 20%. We set carbon membrane as anode to treat the effluent water from the cathode chamber. The rejection of SO42- and Na+ reached to 100 and 88.86%, respectively. The energy consumption was as low as 1.90×10−2 kWh m−3, which was one order of magnitude lower than that reported in the literature. The working principle of ECMD is shown in the Fig.1. High salt rejection can be achieved since the water molecules only overcome low energy barriers in confined space, while huge inherent dehydration energy was required for hydrated ions to enter the nanochannels leading to the removal of salt ions. Additionally, carbon membrane with additional electric field can be used as an integrated membrane electrode combining the effects of confinement and electric potential gradient. Such membrane electrode can repel co-ions and attract counter-ions using pressure as the driving force for mass transport. The ECMD made the desalination process concentrate on adsorption desalination (AD), capacitive deionization (CDI) and electric enhanced confinement membrane desalination (CMD). A series of experiments were conducted to determine the contribution of processes. It was found that SO42− removal could be achieved 38.62% by AD, 18.50% by CDI and 80.99% by CMD, respectively, which suggests that high desalination efficiency was stemmed from multi-effects but mainly from electro-confinement. ECMD will be a promising energy efficient method for salt rejection.